1. FIELD OF THE INVENTION
The present invention relates to electrical switches, and more particularly, to optical switches for use in keyboard applications.
2. BACKGROUND ART
Switches for keyboard applications typically rely upon an electrical coupling of metallic contacts to provide the desired switching action. Such contacts are prone to corrosion, dirt buildup, and metal fatigue. Consequently, the service life of switches employing such contacts is limited.
The term "optical switch" is commonly applied to a switch that includes an emitter of electromagnetic radiation, typically a light emitting diode (LED), and a photo-detector that is sensitive to the emitted radiation. The output of the detector is coupled to an electronic switch within an electrical circuit. The optical path between the emitter and detector may be selectively interrupted, thereby closing or opening the electrical circuit. Such switches do not suffer the drawbacks of mechanical electrical contacts. However, such optical switches typically do not provide a user with the tactile and audible feedback that has been found desirable for switches used in keyboard applications.
It has been known to adapt switches with mechanical contacts to enhance the tactile and audible feedback provided to the keyboard operator. For example, U.S. Pat. No. 4,341,934 entitled "Actuator for Keyboard Switches" issued July 27, 1982 to Muller and U.S. Pat. No. 4,525,613 entitled "Spiral Spring Keyboard Switch with Hairpin Spring Tactile Feedback" issued June 25, 1985 to Butts both describe switches specifically designed to provide positive user feedback. Both of the above-referenced patents, however, employ mechanical contacts for accomplishing the switching action.
As will be subsequently described, the present invention comprises an inherently reliable optical switch that also provides a positive tactile feel and an audible click to the user.